1. Field of the Invention
This invention relates generally to ground proximity warning systems for aircraft, and more particularly to warning systems for rotary wing aircraft such as helicopters that provide a warning to the pilot of the aircraft if the flight conditions are such that the tail of the aircraft is in danger of striking the ground.
2. Description of the Prior Art
Ground proximity warning systems for rotary wing aircraft such as helicopters, including systems that warn the pilot of an imminent tail strike, are known. Examples of such systems are disclosed in U.S. Pat. Nos. 3,979,717 and 4,027,838. The systems disclosed in the aforementioned references monitor the altitude above ground and pitch of the aircraft and generate a warning in the event that the pitch of the aircraft is excessive for the altitude at which the aircraft is flying. The systems also monitor the rate of descent of the aircraft and raise the altitude at which the warning is generated as a function of the descent rate to assure that the warning is generated early enough to give the pilot sufficient time to take corrective action. Other systems vary the altitude at which the warning is generated as a function of the vertical movement of the tail of the aircraft, which is a function of both the descent rate and the pitch rate further to improve the warning time.
While these systems do provide a warning to indicate that a tail strike is imminent, they also tend to generate false or nuisance warnings under normal flight conditions when there is no real danger of the tail striking the ground, thus losing their effectiveness because pilots then tend to ignore real warnings.